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What am I doing wrong?


jcal74
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Problem:

  • Difficult to complete 6-star alignment process with CPWI, Cartes du Ciel and ASTAP without sudden wrong slewing problems
  • Even when alignment is successful, mount poorly tracking even after an All-Star Polar Alignment.

Here is my set-up and my workflow:

Set-up:

  • Celestron EdgeHD 8” Scope
  • Advances AVX Mount
  • Polar scope
  • Finder scope
  • Dew Shield (Velcro wrap)
  • Bahtinov Mask
  • T-Ring adapter
  • Nikon D610 (Full frame DSLR)
  • Backyard Nikon
  • Cartes du Ciel
  • ASTAP
  • CPWI to control Mount via hand controller

Workflow

1) Manually align finder scope and telescope

2) Manual polar alignment via polar scope and using the Azimuth and Latitude adjustment Knobs.

3) Launch Backyard Nikon:

  • Correctly configured to interface with CPWI (ASCOM.CPWI.Telescope)
  • Correctly configured to interface with Cartes du Ciel and ASTAP
  • Connected to Nikon D610 via USB

4) Focus using Bahtinov Mask.

5) Mount Hand Controller connected to Laptop.

6) Launch all the following software

  • Carte du Cliel
  • ASTAP (Filed of view height set correctly to 0.65)
  • CPWI

7)      Connect CPWI to hand controller

😎      Select Manual Alignment in CPWI

9)      Set Date and Time in CPWI

10)   Set Location in CPWI

11)   Start Alignment

12)   Ensure RA and Dec are in Index position.

13)   Proceed to select 1st Alignment Star in CPWI (e.g. Arcturus)

14)   Slew to Arcturus in CPWI. Mount slews.

15)   Go to Carte du Ciel and select Arcturus

16)   In Backyard Nikon under Imaging, select Advanced Mode

17)   Click the arrow next to Cartes du Ciel and Arcturus appears in the Target Name Field.

18)   Click Center

19)   Mount slews, Takes a picture and successfully solves within seconds. At this point:

  • Note that nothing else happens I was expecting it to take another picture automatically and slew again, take another picture and slew again until the star is in the center. But nothing happens.
  • So I click center again. Mount slews again, takes a picture and successfully solves again.
  • I do this several times. Until Arcturus finally appear in frame and is close to the center.

20)   Once Arcturus is close to the center, I use the controls in CPWI to perfectly center the star.

21)   Then I click Centered in CPWI

22)   Select another Star for alignment and repeat the process.

23)   This is where the problems sometimes happen. For example:

  • At the 5th star (close to finishing alignment) I’ll select for example Deneb
  • I proceed to click Center in Backyard Nikon as I normally would to solve and center the star.
  • The first time I click center, the mount Slews to the correct area in the sky, takes a photo and successfully solves.
  • Now, I click center again as I have been doing, to get the star to the center. Suddenly, the mount slews to a completely wrong area of the sky.
  •  I click abort.
  •  I try to get the mount to correct itself by returning to CPWI and try to get it to slew back to the correct area, but now CPWI is completely confused as well and points in the wrong area too.
  • So I am forced to cancel the alignment and be extremely discouraged.

The 2nd Problem I have is:

1)      I have successfully completed the 6 star alignment process using the steps above.

2)      Then I proceed to do an All-Star Polar Alignment and successful follow the steps to first slew and center a star and then center the star using the Azimuth and Latitude adjustment Knobs.

3)      I should now be properly Polar Aligned

4)      I take a 30 sec Photo = Stars are streaking

5)      I take a 15 sec Photo = Stars are streaking

6)      I take a 5 sec Photo = Stars are streaking

7)      I take a 2 sec Photo = Stars are not round.

What am I doing wrong?

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6 answers to this question

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Trying to learn how to image with a slow telescope like an 8" f/10 SCT is difficult. I used an 8" EdgeHD and when I was first trying to teach myself how to image and almost gave up on imaging. Then I bought a 5" f/5.2 refractor and immediately had success. The refractor was much easier to image with. I have hardly used the SCT since then.

Just so there is no confusion.

1) doing a 6-star alignment is not a polar alignment, nor is it a substitute for a polar alignment. Polar alignment is adjusting the mount in azimuth and altitude until Polaris is in the correct location when the mount is at the index position in both the RA and Dec axes. In order to adjust the azimuth and altitude, the mount cannot be tracking!

2) Say you do a rough polar alignment with a polar finder scope, or by looking, with your eyes, up through the polar axis and using the altitude and azimuth adjustments to center the Polaris. Then you do a 4-star alignment. Then you slew to Arcturus, or some other bright star, and do an All Star Polar Alignment. When the ASPA is done, you need to restart the mount and do the 4-star alignment again. This is because you invalidated the previous 4-star Alignment when you adjusted the altitude and azimuth.

3) If you have a rough polar alignment and a good 4-star alignment, the mount should find objects with the hand controller and they should stay in the  eyepiece for at least several minutes without drifting too far. If the object drifts in RA, then your tracking rate may be incorrect. If the object drifts in Dec, then it indicates that you are not accurately aligned to the Celestial North Pole. There are several tools that can help improve your polar alignment Tools like BYN's Drift Alignment tool, PHD's Drift Align tool, PoleMaster from QHYCCD. If you can't slew to targets and keep them in the FOV for several minutes, then either the mount is malfunctioning, the date and time settings are incorrect, or some other part of your setup process was not done correctly.

4) If you think that you are well aligned, but when you slew to a target the pointing is "way off". The usual culprit is incorrect settings in the mount for the observing site latitude, longitude, perhaps elevation, date, time, time zone offset, daylight saving flag. All of those have to be set correctly. They also need to be correct in CPWI, CdC, and every other application that is connected to the mount. The DST flag is not whether your observing site uses DST. It is whether it is currently using DST.

5) If you are well polar aligned and tracking at the sidereal rate, there should be no visible elongation of stars in a 30-second or shorter exposure, even with an 8" f/10 SCT. Use the arrow keys on the hand controller to get an idea of whether the drift is in RA or Dec. For example if the stars drift to the right, and you can move them back to the left with either the left or right arrow keys, then you are not tracking at the sidereal rate. If the stars drift up or down and you adjust back to center with the up/down arrow keys then your polar alignment is off.

6) Delay connecting any software to the mount until you are able to slew to targets and see them near the center of the FOV with just the hand controller, or CPWI. If you need to use CPWI to do your alignment, then don't connect ASCOM clients (CdC, ASTAP, BYN, etc) to CPWI until you are able to slew and hit targets with CPWI.

I hope this helps.

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First, thank you for taking the time to respond, it's very much appreciated.

I'm not going to give up!

Yes, I start the process with a rough polar alignment with a polar scope by adjusting the mount in azimuth and latitude using the knobs on the mount.

From your advice I will try the following:

  • Restart the mount and do another 4-star alignment again after an ASPA is completed.
  • I know the correct latitude, longitude, date, time, time zone offset, daylight saving flag is set correct in CPWI and therefore I know the mount is supposed to be set-up correctly. However, I didn't set any of these in CdC or ASTAP  so I will check if I can set these in those applications.
  • You suggest to not connect ASCOM clients (CdC, ASTAP, BYN, etc) to CPWI until I am able to slew and hit targets with CPWI. However, my DSLR is essentially my eyepiece and I can't really see any stars without the help of BYN, CdC and ASTAP. Any suggested workflow on how to do this, given that it is difficult to see anything with my DLSR to perform an alignment?

Any other workflow suggestions would be welcomed.

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15 hours ago, jcal74 said:
  • Celestron EdgeHD 8” Scope
  • Advances AVX Mount

This is a Good Long Focal-Length Scope on a Moderately Capable Mount.  It CAN work for AP Imaging - I've Imaged with my C9.25 on both my AVX and CG5-AGT.  And I use a very similar Alignment Workflow.

BUT not without AutoGuiding!!  Even for a much lesser focal length 480mm 80mm Refractor, the AVX really needs AutoGuiding for Exposures over 45sec.

Your next addition to your kit should be a GuideScope - it can be sized to replace the 9x50 Finderscope since you are using PlateSolving to Slew and Center Alignment Stars - and a decent moderate Guide Camera such as the ZWO ASI120MM or MC Mini or the older "regular ASI120 (still widely available though officially discontinued).  Add PHD2 as your AutoGuiding Software - integrates with CPWI and BYE/BYN - and you'll be able to expect 2-4 minutes Exposures. 

The good news is the Guide Camera - especially if you go with the OSC version - can also be used as a Planetary Video Camera (no need for AutoGuiding for such a Target and will do better than ANY NIKON DSLR).

Welcome to AP Imaging - it is the culmination of several "systems" working together to provide the extreme accuracy required to get and keep your Camera pointed at the exact right spot in the Vastness of Space...

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Thank you, this is definitely where I intend to eventually head in AP journey (Auto guiding with precision). However, since the learning curve is so steep, before I invest more $$. I really want to succeed in proper aligning and tracking with the set up I have now. I would be happy to get 15 second shots with no trails. Once I succeed with that, I will feel better that I can go to the next budget level.

I will keep at it. I'll get it eventually.

Thank you for the advice. 

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For unguided DSO Exposures, realize that you will need to allow any native Backlash of the AVX geartrains to be taken-up.  This means that the first 1-2 minutes are more likely to have Backlash-related trailing (as well as Polar Alignment Error Drift).  Then, once Backlash is taken-up, you may have your best exposures. 

This can be mitigated to a degree by how well you Balance the Scope on the Mount.  YouTube is helpful to explain Balancing - and (slightly) West-Heavy Balancing in RA to minimize RA Backlash.  While everybody has a "Trick" for DEC Balancing, most are really only effective once you are AutoGuiding.

But, realize that with a Scope as Heavy and Long-Focal Length as the EdgeHD 8, there is little help for AP Imaging without AutoGuiding. (It just is...)  The Good News is that AutoGuiding in general is easier (but separate) than Polar Alignment...

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